The present invention generally relates to Superconducting Quantum Interference Devices (SQUIDS) and to a particular SQUID type called a HYBRID SQUID.TM.. The present invention particularly relates to the geometry of the construction of conical coupling cavities within a superconducting canister holding a circular, toroidally wound, input coil, which coil is inductively coupled to a SQUID which consists of Josephson junctions upon a substrate.
The prior art to the toroidal canister with a conical cavity of the present invention is a toroidal canister with a non-conical cavity utilized in the HYBRID SQUID.TM. (direct current and radio frequency types), which is the trademark and commercial offering of S.H.E. Corporation, 4174 Sorrento Valley Boulevard, San Diego, Calif. 92121. Specifically, the prior art structure teaches the inductive coupling of large volume (large radius) circular toroidally wound input coils to a small SQUID upon a chip substrate via an inductive coupling cavity which is not direct and straight, but which cavity within the toroidal superconducting canister actually undergoes a right angle bend.
Although possibly easier of being machined in superconducting materials such as niobium and niobium titanium (which materials present difficulties to precision machining), the prior art canister is not possessed of the optimum coupling cavity geometry for keeping those stray inductances arising from the coupling of a small radius SQUID to a large radius coil (the toroidally wound input coil) optimally small. It is desired that the stray inductance coupled to the SQUID should be minimized in order to improve the noise performance of the SQUID.